1. Field of the Invention
The present invention relates to a focus adjusting system, an image capture apparatus and a control method thereof, and is suitable for coping with such a situation that a large quantity of image shake (commonly called “camera shake”) occurs in an object image taken by the image capture apparatus because of, for example, an unsteady hand of the apparatus user.
2. Description of Related Art
The current trend in automatic focusing apparatuses for video cameras is to use an AF (automatic focusing) evaluation value for focus adjustment. The AF evaluation value is detected as the sharpness of a taken picture from a video signal obtained by photo-electrically converting an object image via an image capture element or the like. Then, the position of a focusing lens is controlled to make the level of the AF evaluation value maximum.
As the AF evaluation value, use is generally made of the level of a high-frequency component of the video signal that is extracted by a band-pass filter having a given bandwidth. When an ordinary object image is taken, the level of the AF evaluation value increases as the focusing lens approaches an in-focus point, as shown in FIG. 2. The in-focus point is considered to be the position of the focusing lens where the AF evaluation value has reached a maximum level.
In addition, some video cameras are equipped with an image stabilizing apparatus. The image stabilizing apparatus detects the quantity of image shake of a taken picture by sensing a signal from an angular velocity sensor such as a vibration gyroscope or by detecting motion vectors from an image signal, and compensates for image shake optically or electronically on the basis of the quantity of image shake detected.
In such a video camera capable of detecting image shake, information on image shake can be utilized for controlling automatic focusing. For example, Japanese Laid-Open Patent Application No. Hei 10-322583 (page 6 and FIG. 2) proposes that automatic focusing be inhibited as long as a large quantity of image shake occurs.
However, the above proposal has the following problem. If automatic focusing is suspended as long as a large quantity of image shake occurs, automatic focusing cannot respond to changes in object distance that may take place during such a period.